1. Field of the Invention
This invention relates to fluid control systems for surgical irrigation and aspiration and more particularly to fluid control systems for use with an ultrasonic surgical tool which includes means for irrigation of a surgical site and means for aspiration of fluid from the surgical site.
2. Description of the Prior Art
Intraocular surgery, and removal of cataracts in particular, has been greatly aided by the development of surgical instruments which include cutting or fragmenting means combined with means for irrigating the intraocular surgical site and aspirating therefrom the irrigating fluid together with any tissue fragments produced by the surgical procedure. One instrument of this type is disclosed in U.S. Pat. No. 3,589,363, to Banko et al. The surgical instrument therein disclosed comprises a handpiece which holds an elongated ultrasonic surgical tool and contains means for exciting longitudinal ultrasonic vibrations in the tool. The vibrating tool when applied to a tissue such as the crystalline lens of the eye which has developed a cataract is capable of breaking the tissue into small pieces. The tool is provided with means for supplying an irrigating fluid to the surgical site and aspiration means for removing irrigation fluid and fragmented tissue from the surgical site. The aspiration means includes an axial bore through the ultrasonic tool which is connected to a source of suction whereby the tissue fragments are aspirated from the surgical site, together with the irrigation fluid. Because the ultrasonic surgical tool of this patent fragments the excised tissue into very small particles, which are removed with the spent irrigation fluid, the incision in the eyeball need be only large enough to insert the tool and is substantially smaller than the incision required for removing the lens in one piece. However, since the surgical wound in the eyeball is only large enough to insert the ultrasonic surgical tool and irrigation means, the surgical field is practically entirely enclosed, and controlling the flow of irrigation fluid and aspiration fluid is very important. In particular, the suction applied to the aspiration means must be limited to a safe value, to avoid the danger of collapsing the eyeball. The fluid control system disclosed by Banko et al. is operated by the surgeon and comprises an aspiration pump and electrically operated value means for connecting and disconnecting the suction inlet of the pump to the aspiration tubing which conveys fluid away from the surgical field. The valve is controlled by the surgeon by means of a foot switch.
An improved fluid control system is disclosed by Kelman, U.S. Pat. No. 3,693,313. This apparatus addresses the problem of maintaining the proper pressure in the enclosed surgical field even with the occurrence of blockages in the aspiration conduit. A blockage of occlusion may occur, for example, when a piece of fragmented tissue which is larger than the axial bore of the surgical tool is drawn against the entrance to the axial bore in the tool. When such a blockage occurs in the aspiration line, the negative pressure or suction in the aspiration conduit between the surgical site and the vacuum pump increases. If the blockage is then suddenly released either by the mechanical action of the ultrasonic tool or by the increased value of the suction force, there is a tendency for the fluid within the surgical site to rush suddenly into the aspiration conduit with perhaps disastrous consequences. This is an especially important problem in ocular surgery because the total volume of the fluid in the surgical site is smaller than the volume of fluid in the irrigation and aspiration lines. Accordingly, the flow control system of Kelman, U.S. Pat. No. 3,693,613 provides for automatic rapid equalization of the pressure in the aspiration conduit when occlusion is removed. This is accomplished by providing a flow-sensitive transducer in the aspiration conduit which senses the rate of fluid flow and generates an electrical signal which is sent to a controller. Whenever the flow rate increases suddenly, indicating that a blockage has just been cleared, the controller causes a vent valve in the aspiration conduit to open at once, thus relieving the suction and preventing excessive withdrawal of fluid from the surgical site.
The flow control system of Kelman, U.S. Pat. No. 3,693,613 is effective but somewhat complicated. Accordingly, another flow control system for surgical devices of this type was developed by Weiss, et al., U.S. Pat. No. 3,902,495. In this system irrigation fluid is supplied to the surgical site from a source of fluid via an irrigation conduit provided with a pressure relief valve to prevent the irrigation pressure from becoming too high. Similarly, the aspiration conduit is provided with a relief vent valve which opens to the atmosphere at a preset pressure differential, thereby preventing the suction in the aspiration conduit from exceeding a preset value. In this way, the suction in the aspiration line never exceeds a predetermined preset value, and the surgical site is not exposed to excess suction when a blockage is cleared.
Another variation of the method of U.S. Pat. No. 3,693,613 is disclosed in Banko, U.S. Pat. No. 4,496,342. In Banko's apparatus irrigation fluid is supplied to an enclosed surgical site such as the interior of the eye and withdrawn from the surgical site through an aspiration conduit. A flow-sensitive transducer in the aspiration conduit senses the sudden increase in flow rate which occurs when a blockage in the aspiration tube is released and actuates a valve which releases fluid from a second source of fluid into the aspiration line. At the same time, the aspiration pump is shut off until the flow rate has returned approximately to normal. In this way the surge of fluid out of the eye when an aspiration line blockage is released is greatly diminished.
While these flow control systems are effective, they have not addressed the problem of releasing the blockage itself. At best they have limited the suction to a maximum value or sensed the flow surge after the blockage is released and reduced the surge. They have not incorporated the capability of sensing the blockage and then rapidly and positively, under control of the surgeon, equalizing the pressure in the irrigation and aspiration lines for rapid clearing of a blockage.
Hence a need has continued to exist for a fluid control system for a surgical irrigator/aspirator wherein the excess vacuum in the aspiration tubing after a blockage can be controllably and rapidly released.